1. Field
The present invention relates generally to systems and apparatus for irradiating targets with electromagnetic radiation, and more specifically to systems having annular-type or various sectored applicators and associated control systems for controlling application of radiation to targets through phased array power steering, wherein the phased array system is integratable with a magnetic resonance imaging system.
2. State of the Art
Current systems for applying electromagnetic radiation (EMR) to targets, such as living bodies and biological tissue, and controlling the position of a region of heating within the target through phased array power steering are provided with a plurality of electromagnetic applicators powered by multi-channel EMR systems where different applicators are each provided with electronically controlled power of electronically controlled phase by different power channels of the EMR system. This creates a desired phased array heat pattern steering capability. Such an approach results in high system complexity and cost in order to provide such phased array heat pattern steering. The phased array devices have been integrated with magnetic resonance (MR) imaging systems and operated simultaneous and independent of the MR imaging system.
Several types of therapeutic treatments for cancer in humans are in current, common use. These treatments include surgery, X-rays, radiation from radioactive sources, and chemotherapy. These treatments are often combined in various ways to enhance treatment effectiveness.
Although such conventional treatment techniques have been successful in treating cancer in many patients and in prolonging the lives of many other patients, they are frequently ineffective against many types of cancer and often have severe adverse side effects at the necessary treatment levels. Protracted treatment of cancer patients by X-rays or chemotherapy, as an illustration, tends to eventually destroy or inhibit the patients' natural immunological systems to an extent that many patients eventually succumb to common infectious diseases, such as influenza or pneumonia, which otherwise probably would not be fatal. Also, many patients having advanced stages of cancer or complications may become too weak to withstand the trauma of surgical or other cancer treatments; hence, the treatments cannot be undertaken or must be discontinued.
Due both to the prevalence and the typically severe consequences of human cancer, as well as frequent ineffectiveness of current treatments such as those mentioned above, medical researchers are continually experimenting in an attempt to discover and develop improved or alternative cancer treatment methods with their associated treatment apparatus.
Hyperthermia, the generation of artificially elevated body temperatures, has recently been given serious scientific consideration as an alternative cancer treatment. Much research has been conducted into the effectiveness of hyperthermia alone or in combination with other treatment methods. This research is important in that hyperthermia techniques appear to have the potential for being extremely effective in the treatment of many or most types of human cancers, without the often severely adverse side effects associated with current cancer treatments. Hyperthermia is sometimes called thermal therapy indicating the raising of the temperature of a region of the body.
Researchers into hyperthermia treatment of cancer have commonly reported that many types of malignant growths in humans can be thermally destroyed, usually with no serious adverse side effects, by heating the malignancies to temperatures slightly below that injurious to most normal, healthy cells. Furthermore, many types of malignant cell masses have reportedly been found to have substantially lower heat transfer to lessen the ability to dissipate heat, presumably due to poorer vascularity and reduced blood flow characteristics. Consequently, these types of growths appear capable of preferential hyperthermia treatment. Poorly vascular malignant growths can reportedly be heated to temperatures several degrees higher than the temperature reached by the immediately surrounding healthy tissue. This promises to enable hyperthermic treatment of those types of malignant growths which are no more thermally sensitive than normal tissue without destruction of normal cells, and additionally to enable higher temperature, shorter hyperthermia treatment times of more thermally sensitive types of malignancies which exhibit poor vascularity, usually an advantage for important medical reasons.
In this regard, researchers have commonly reported that as a consequence of these thermal characteristics of most malignant growths and the thermal sensitivity of normal body cells, hyperthermia temperatures for treatment of human cancer should be carefully limited within a relatively narrow effective and safe temperature range. Hyperthermia is generally provided by temperatures over 40 degrees C. (140 degrees F.). Hyperthermia has historically included temperatures well above 60 degrees C., but in recent years has generally been considered to include temperatures as high as 45 degrees C. (113 degrees F.). However, there may be portions of a cancerous tumor that will exceed this level, the intent is to attempt to get as much of the tumor region above the 40 degree C. region as possible.
At treatment temperatures above the approximate 45 degrees C. (113 degrees F.), thermal damage to most types of normal cells is routinely observed if the time duration exceeds 30 to 60 minutes; thus, great care must be taken not to exceed these temperatures in healthy tissue for a prolonged period of time. Exposure duration at any elevated temperature is, of course, an important factor in establishing the extent of thermal damage to healthy tissue. However, if large or critical regions of the human body are heated into, or above, the 45 degree C. range for even relatively short times, normal tissue injury may be expected to result.
Historically, late in the last century alternating electric currents at frequencies above about 10 KHz were found to penetrate and cause heating in biological tissue. As a result, high frequency electric currents, usually in the megahertz frequency range, have since been widely used for therapeutic treatment of such common bodily disorders as infected tissue and muscle injuries. Early in this century, the name “diathermy” was given to this EMR tissue heating technique, and several discrete EMR frequencies in the megahertz range have subsequently been allocated specifically for diathermy use in this country by the Federal Communications Commission (FCC).
Extensive articles and reports have been written on the use of the phased array principle to provide hyperthermia heat pattern steering, and several patents have been issued covering use of phased arrays. All have relied upon the use of electronic phase and power steering to provide heat pattern steering control. This results in relatively complicated equipment configurations with multiple channel controls of power and phase. Such configurations can be difficult for routine clinical professionals to learn and utilize in the clinic. The simpler the clinical controls are in such a treatment system, the easier the operation of the system and potentially the greater the reliability. Simplicity of such designs may further lead to fewer system failures due to component failures. The utilization of standardized heating regions provided by standard energy steering configurations is expected to provide improved adaptation for clinical use.
The BSD-2000 system produced by BSD Medical Corporation, Salt Lake City, Utah, utilizes multi-channel phased array systems that control frequency, radiated power, and relative phase. Each channel has electronic controls of power and phase and is connected to different antennas. This allows electronic steering of the heating pattern, but at high cost and complexity. Such high cost can be cost prohibitive for routine clinical use. The ability to do heat pattern steering permits energy to be focused and directed more selectively to the target tumor region. In order to provide sufficient heat energy penetration, a lower frequency must be selected. This is because the penetration attenuation of human tissue increases at higher frequencies. As frequency is lowered however, the heating focus diameter increases. Thus, the proper frequency is needed to provide the optimum depth within acceptable heating pattern size limits. In general, hyperthermia is best applied when tumor target tissues around the diseased area is also heated. This provides preheating of inflowing blood and reduces thermal conduction from the perimeter of the tumor to draw heat out of the tumor perimeter. The BSD-2000 system has been investigated since 1988. The novel use of such phased arrays systems has proven to be useful and beneficial in treating patients with various forms of cancers, even in Phase III clinical trials. However, the use of complex and expensive multi-channel amplifier systems to provide multiple EMR synchronous phase energy channels that have phase control to steer the heating region in the body has excessive complexity for routine clinical use in some treatment centers. The BSD-2000-3D/MR system is the integration of the BSD-2000-3D hyperthermia system with a magnetic resonance imaging system. In such a configuration the hyperthermia system has been operated independent of the MR imaging system, where the MR imaging system has been used as an independent monitor primarily of temperature. This has been done using the proton resonance shift from the image stored prior to body heating and digitally subtracting the phase image of the initial pattern from the complex phase image patterns obtained during heating. This provides generally a dominant indication of the temperature change in tissues of the body. This temperature change image produced by the MR imaging system can include error effects that are produced by tissue perfusion changes during heating treatments. The perfusion changes can also be determined by the MR imaging system.
There is a need for EMR applicator apparatus, and corresponding methods for EMR irradiation, which provide simplified heat pattern steering of EMR heating in a target, such as a target of biological tissue in a living body or tissue simulating matter.